This invention relates to composite diamond abrasive compacts.
A composite diamond abrasive compact consists of a diamond compact bonded to a cemented carbide substrate or support. Such compacts are well known in the art and have been described extensively in the patent and other literature. They have also found wide commercial application.
Composite diamond abrasive compacts are generally manufactured by placing a layer of diamond particles on a cemented carbide body to form an unbonded assembly and then subjecting that unbonded assembly to elevated temperature and pressure conditions at which diamond is crystallographically stable. Cobalt from the carbide substrate infiltrates the diamond mass during the compact manufacture. In so doing, the carbide substrate is depleted of cobalt giving rise to stresses in the substrate. These stresses can lead to failure of the composite compact, e.g. delamination of the diamond compact and carbide support layers, during treatment in furnace brazing.
U.S. patent specification No. 3,745,623 describes a method of making a composite diamond abrasive compact. In one embodiment of the method, there is not a sharp transition from a carbide-cobalt powder mix (for the carbide substrate) to the diamond powder mix. Instead, a transition layer between the carbide-cobalt mass and the diamond layer may be provided, that transition layer containing both carbide-cobalt powder and diamond grit in a gradated mix to minimise stress concentrations.
U.S. Pat. No. 4,802,895 describes a method of making a composite diamond abrasive compact in which a thin layer of fine carbide powder is placed on a surface of a carbide body and a mass of fine diamond particles mixed with powdered cobalt placed on the layer of carbide powder. That unbonded assembly is then subjected to the usual conditions of elevated temperature and pressure to produce the composite diamond abrasive compact.
U.S. Pat. No. 4,311,490 describes a method of making a composite diamond abrasive compact in which the diamond mass consists of two layers, a coarse layer being closest to the catalyst metal, i.e. the cobalt, and the finest layer being disposed furthest away from the catalyst metal. The source of cobalt is the carbide substrate.
U.S. Pat. No. 4,403,015 describes a method of making a composite abrasive compact in which there is an intermediate bonding layer between the compact and the carbide substrate. This intermediate bonding layer comprises cubic boron nitride in an amount of less than 70 volume percent and the residual part principally consisting of a compound selected from among carbides, nitrides, carbonitrides or borides of IVa, Va, VIa transition metals of the Periodic Table, an admixture thereof, or a mutual solid solution compound thereof.